1. Field of Invention
The present invention is directed to devices and methods of using a surgical drain to monitor internal tissue condition, and more particularly to a surgical drain having at least one sensor for monitoring the condition of a tissue proximate to the surgical drain.
2. Description of Related Art
It is desirable for a physician to know the condition of tissues or organs (hereafter referred to interchangeably) within the patient's body particularly after trauma or surgical manipulation. Since such tissues may reside under the skin or within a body cavity, a physician must invasively inspect the tissue (such as by surgery, including laparoscopy), or use indirect measures to assess an organ's condition (such as radiological, blood testing and patient accounts of sensations of illness or pain). However, these methods can be disadvantageous. An invasive examination may cause discomfort and risk of infection to the patient, and the information obtained either through direct inspection or indirectly via blood or radiological analysis, may be relevant only to the time at which the procedure is performed, and examination may render only indirect information about the physiological condition of the organ.
Monitoring of organ function can be important after surgeries such as organ transplantation, resection, cryosurgery and alcohol injection. Surgical complications, such as vascular complications, may disrupt adequate oxygen circulation to the tissue, which is critical to organ function and survival. Following liver surgery, for example, a physician may draw patient blood to determine the condition of the organ by measuring liver enzymes (such as transaminases) and clotting factors (such as prothrombin). Unfortunately, these blood tests reflect liver condition only at the time the blood sample is drawn, and changes in these laboratory values can often be detected only after significant organ damage has already occurred, permitting a limited opportunity for intervention by the physician to improve the condition of the organ or find a replacement organ in case of transplantation for the patient.
Other methodologies have been used to assess internal tissue conditions. For example, (1) imaging and Doppler techniques, (2) optical techniques, and (3) thermodilution have been used to measure tissue oxygenation and/or perfusion. However, these techniques can be difficult to successfully apply to continuous monitoring of organ condition, and may provide only qualitative or indirect information regarding a condition, and/or may provide information about only a small segment of an organ.
Imaging and Doppler Methods. Angiography may be used for determining the location and extent of blood flow abnormalities in major hepatic vessels, such as hepatic artery or portal vein stenoses and thromboses. Similarly, Doppler sonography may be used for the evaluation of blood flow in the hepatic artery and the portal vein. These methods can lack the sensitivity and the resolution necessary for assessing hepatic microcirculation. Contrast sonography has been applied for qualitative assessment of blood perfusion in the microvasculature, but its potential for quantitative measurement is still unclear. Although sonography can be performed at bedside, it is neither sensitive nor specific, and does not indicate the actual tissue oxygenation. It is usually used as a screening for the more invasive angiography. Angiography is still a preferred clinical standard in determining vessel patency for any organ such as blood flow abnormalities in major hepatic vessels, such as hepatic artery or portal vein and may visualize stenosis or thrombosis in these and other vascular structure. This test however is invasive and requires the injection of contrast material with its side effect of allergic reaction, kidney failure and fluid overload. The test cannot be performed at bedside (as in Doppler Ultrasonography) and requires moving critical ill patient to the radiology suite, and the side effects are also higher in these sick patients.
Other imaging methods, such as Spiral Computer Tomography (CT), three-dimensional magnetic resonance, angiography and radionuclide scintigraphy using Technetium 99 m sulfur colloid may be used to assess blood flow to organs such as the liver following liver transplantation. However, these methods may not be sufficiently sensitive to obviate angiographic assessment, as described above. Further, these methods can also be limited in their ability to measure blood perfusion in microvasculature of the tissue. Although blood may be circulating to large vessels, it is oxygenation and perfusion at the capillary level, which often maintains the health of the entirety of the organ. By the time larger vessels are visibly impaired, the organ may have already undergone significant tissue damage. Further, these methods may be invasive in requiring the infusion of dye to which patients may react. Finally, for each dye injection, the organ condition may be assessed for a given interval. If further monitoring is needed, additional dye injection and repeated imaging may be required.
Laser Doppler flowmetry (LDF) has been used to measure blood flow in the hepatic microcirculation, but may not be able to provide information about the tissue oxygenation or blood content. LDF is also limited in its application due to the short depth of penetration and the large spatiotemporal variations of the signal obtained. Therefore, this technique may not reflect information regarding a broad geography of the tissue, and large variations may occur in recordings from different areas, in spite of tissue conditions being similar between the regions.
Thermodilution. Thermodilution technology has also been used for monitoring tissue perfusion. One example is the Bowman perfusion monitor, which uses an invasive catheter probe to measure hepatic perfusion. The probe may be inserted into the liver and a thermistor in its tip may be heated to remain slightly above tissue temperature. The local perfusion may be estimated from the power used in heating the thermistor to few degrees above tissue temperature to induce local dilation of the blood vessels. This can lead to a false perfusion measurement that is higher than the actual perfusion away from the probe. The latter source of error may not be corrected by calibration because the degree of vasodilation per temperature rise may vary between patients and may depend on many factors including administered drugs.
Thermodilution techniques may also be disadvantageous at least in requiring the insertion of catheter probes into an organ, which can become impractical when multiple probes are to be used.
Perfusion detection techniques such as LDF and thermodilution have an additional common inherent limitation. These methods may not measure tissue oxygenation, which is more relevant than perfusion in determining tissue viability. Perfused tissue can still suffer ischemia, oxygen deprivation, depending on the oxygen demand by the tissue versus its availability in the blood. For example, the liver has a dual blood supply from the hepatic artery and the portal vein. The blood flowing from the portal vein into the liver carries much less oxygen to the hepatic tissue than that from the hepatic artery. An occlusion of the hepatic artery would not cause a significant drop the hepatic perfusion, however, it would cause a drastic drop in the oxygenation. Hence, monitoring the hepatic perfusion only would be a misleading measure of ischemia. Further, this critical demand-availability balance can be easily disturbed due to immunogenic and/or drug reactions, therefore monitoring of oxygenation levels is important in monitoring tissue condition.
Optical Methods. Conventional optical techniques for the detection of tissue ischemia include fluorescence and transmission methods. Ischemia leads to anaerobic respiration and the accumulation of the reduced nicotinamide coenzyme NADH. The concentration of NADH may be detected optically because it is autofluorescent and has peak excitation and emission wavelengths at about 340 nm and 470 nm, respectively. Therefore, the fluorometric properties of NADH can be used to monitor and quantify this marker of ischemia.
However, this technique may not have been applied clinically due to several concerns. First, the fluorescence of NADH can be strongly modulated by the optical absorption of tissue hemoglobin, and the absorption of hemoglobin varies with its state of oxygenation, which can complicate the analysis of the data. These modulations can mask the actual intensity of NADH fluorescence thereby causing inaccuracies in the evaluation of ischemia. Further, this method may be disadvantageous at least in that repeated exposure of the tissue to ultraviolet light results in photobleaching of the tissue. Therefore, it may not be possible to continuously monitor the same position on the organ for a prolonged period of time (i.e., more than 24 hours). Finally, the above method is only an indirect evaluation of tissue ischemia, as it relies on monitoring abnormalities in the concentration of NADH and may result from other conditions such as generalized sepsis or hypotension.
Optical transmission methods involve the use of visible and/or near-infrared radiation to measure the absorbance of blood in a tissue bed and determine the oxygen saturation of hemoglobin. A common transmission technique is pulse oximetry where red and infrared light from light emitting diodes is transmitted through the tissue, usually a finger or ear lobe, and detected by a photodiode. The oxygen saturation of hemoglobin can be estimated by measuring its optical absorption at predetermined wavelengths that allow the maximum distinction between oxyhemoglobin and deoxyhemoglobin. Researchers have used lasers to illuminate one side of the kidney and detected the transmitted light on the opposite side using a photomultiplier. For example, Maarek et al., SPIE, Advances in Laser and Light Spectroscopy to Diagnose Cancer and Other Disease, 2135:157–165, 1994. A major disadvantage of such techniques is the invasive nature of the procedure to place a tissue sample between the light source and the detector for a single measurement.
Intra-abdominal pressure following major surgery or trauma (such as a car accident, gun shot wounds, combat, or earthquake injuries) may rise to extremely high levels due to tissue edema secondary to the injury, especially following multiple blood transfusions, severe shock or inflammatory responses.
An increase in pressure may lead to severe organ dysfunction, such as kidney failure and acute respiratory failure due to lung compression through the diaphragm. The increased pressure in the abdomen may also lead to a decrease in the venous returns to the heart, therefore, affecting the cardiac output and the perfusion to all organs/tissues leading to a decrease in oxygen delivery.
Early detection of critical intra-abdominal pressure may be corrected by several interventions, including sedating the patient or opening of the abdomen. Prompt restoration of proper intra-abdominal pressure can reverse the consequences described above. However, once a critical point is reached, organs may suddenly fail, which may be irreversible in certain conditions and lead to rapid deterioration of multiple organs and potentially death.
A current method of monitoring intra-abdominal pressure following major surgery or trauma relies on indirect measurement of intra-organ pressure such as the bladder or the stomach pressure. These methods require direct operator intervention and are done only intermittently at a specific timing, such as every 1 to 4 hours, or if the patient shows signs of deterioration.
Current methods of measuring abdominal pressure may carry significant errors due to direct personal intervention, lack of reproducibility and challenges related to the injury itself. For example, a large hematoma or pelvic fracture may affect the bladder pressure directly without relation to the overall intra-abdominal pressure.
As discussed above, each of these methods has significant technical disadvantages to monitoring tissue condition. Further, each of these methods can also be cumbersome and expensive for bedside operation due to the size of the apparatus and cost associated with staff administering these methods, and unsuitable for continuous monitoring of tissue conditions.
Therefore, it is desirable to have a device and methods to aid physicians in predicting problems and complications associated with internal trauma or surgery. It is desirable to have a device which is positionable and removable with relatively minimal effort, minimally invasive and causes minimal discomfort for the patient, provides continuous current information about tissue or organ condition, provides direct information about tissue or organ condition, and/or provides feedback on the effects of interventions, such as medications or other procedures to improve tissue or organ condition.